During the manufacturing of an integrated circuit a number of dielectric films may be deposited. One technique used to deposit dielectric films at temperatures less than approximately 550 C is PECVD (plasma-enhanced chemical vapor deposition). Some PECVD tools are single wafer tools which a deposit dielectric thin film onto one wafer at a time. One important deposition criteria for the dielectric thin film is thickness uniformity across the wafer including the edges of the wafer. In order to provide uniform thickness out to and including the edges of a wafer the deposition may extend beyond the wafer edge. In PECVD deposition processes using pressures greater than about 12 Torr, a ring of deposited dielectric (also called a deposition fence) may form just outside the edge of the wafer on the pedestal or the wafer carrier ring upon which the wafer is positioned. The deposition fence typically presents a particle problem when the thickness builds up after dielectric deposition upon multiple wafers. The deposition fence may peel due to accumulated film stress or the deposition fence may become sufficiently thick to come into contact with the robot slider which transfers wafers into and out of the chamber. When the robot slider comes into contact with the deposition fence, pieces of the deposition fence may break off and redeposit on the wafer resulting in depressed yield.
Several methods have been developed to deal with the deposition fence. One method is to open the chamber and remove the deposition fence after a specified number of wafers have been processed. Another method is to periodically run a plasma clean step such as a NF3 plasma step to etch away the dielectric fence. Both solutions reduce the time that the deposition tool is available for manufacturing thus increasing manufacturing cost.